The invention relates to noise-silencing mufflers.
The invention arose during muffler development efforts, including those directed to solving problems in box-style mufflers, including muffler shell noise and poor muffler silencing. Since cost is almost always a concern, the solution to the two noted problems must also be cost effective. Box-style or stamped mufflers tend to radiate noise from their flat exterior surfaces. This characteristic is called shell noise and is most often a concern because of its harsh sound and adverse effects on muffler silencing. Also of concern with stamped mufflers is overall acoustic effectiveness. Because these types of mufflers are often constrained to a certain size and shape, their physical layout is not always conducive to good silencing.
The present invention addresses and solves the noted problems in a particularly cost effective manner using a simple design. In one aspect the invention enables usage of identical parts within the muffler, which improves manufacturing efficiency and provides a cost reduction. Assembly of the muffler is also easy because the majority of the muffler's internal parts are designed into two cross flow baffles. In accordance with the preferred embodiment, to combat the shell noise problem, the flow from the inlet is directed into one of two interior chambers of the muffler, formed by placing two of the cross flow baffles back to back. By letting the exhaust flow expand first in an interior chamber, the pressure pulses from the engine are less likely to cause exterior shell noise problems since they are damped considerably before reaching the muffler's outer shell. Stiffening bosses may be provided on larger flat areas of the baffles to control internal shell noise. To increase silencing capability, four chambers are created within the muffler by using a twin baffle design, along with two additional volumes between the outer shells and baffles. In one aspect, a horseshoe-shaped cross flow baffle is designed to provide the twin internal silencing chambers with a desired flow path and area between them. The configuration increases the acoustical effectiveness of the muffler.